knowitalls is rigght, i just found this and its from decmeber:

http://www.sciencedaily.com/releases/2008/12/081207134109.htm


but on the ther hand u should have specified knowitalls in the first place.
my idea is brain diseases are a combination of a toxic immune system plus infection plus some some genetic issues, the first one being the most important as we cant change genetics -ad u cant bale all on genetics and its not really possible to totally avoid having things like herpes.